Sealant compositions containing waxes are widely used as effective moisture barriers in coating applications, and particularly as sealants for controlled release fertilizers. The available sealant compositions are typically thermoplastic waxy materials that are cohesive above their melting points and thus require agitation during a cooling step, for example in a fluid bed cooler or a rolling drum, to produce non-agglomerated, free flowing particles. This cooling step adds capital costs for the equipment and added space, and also adds time and energy costs to the process. An effective sealant that does not require a cooling step would reduce costs and simplify the sealant process.
It is known to mix waxes with thermoset polymers, and apply to fertilizer as in U.S. Pat. No. 6,663,686 to Geiger et al, which teaches the addition of an organic wax to a polyol, applying the polyol wax blend to the fertilizer, and subsequently curing the polyol with an isocyanate.
Hargrove et al, U.S. Pat. No. 8,888,887, teaches a controlled release fertilizer coating which is a reaction product of a mixture including an isocyanate and a polyol and also including a modified wax which is an unsaturated wax component that is cross-linked with sulfur, oxygen and/or a peroxide cross-linking moiety, or a mixture or a combination of an unsaturated wax component and a polyhydroxyl compound that is cross-linked with sulfur, oxygen, and/or a peroxide cross-linking moiety.
It is known to use compositions comprising waxes and wax soluble polymers as sealants applied to sulfur coated fertilizers, as in U.S. Pat. Nos. 5,300,135, 5,478,375 and 5,984,994 to Hudson, et al. These compositions are nonreactive wax based thermoplastic materials. To form a free flowing composition, the sealed granules must be cooled with low shear agitation, typically in a fluid bed cooler, after the application and spreading of the sealant on the surface of the sulfur coated fertilizer.
It is also known to apply a sealant composition over polymer coated fertilizers as is taught in U.S. Pat. No. 5,858,094 to Detrick, and U.S. Pat. Nos. 5,538,531 and 5,698,002 to Hudson. The sealants are described as waxes, and the sealed coated fertilizer granules must be cooled after the sealant application, typically in a fluid bed cooler.
U.S. Pat. No. 5,137,563 to Valkanas teaches controlled release coating for fertilizers comprising a mixture of wax and specific wood rosins or dimerized rosins with a high content of conjugated unsaturation. The waxy component is selected from the group consisting of linear or branched paraffin waxes, polyethylene waxes, polyethylene oxide, fat, fatty acids and cellulose products and derivatives thereof preferably having a melting point from 70 degrees C. to 130 degrees C.
U.S. Pat. No. 3,223,518 to Hansen teaches multiple fertilizer coatings that include alkyds, and may include coatings of other polymers and waxes including paraffin and natural and synthetic waxes. The coatings are applied as discrete coats, and the components of the coats are not commingled with the components of preceding or subsequent coatings.
U.S. Pat. No. 3,252,786 to Bozzelli, et al, teaches the addition of a minor portion of oxidized wood rosin and wood rosin derivatives to petroleum wax. Particles of fertilizer materials are dispersed into the wax-rosin mixture and milled to very small particles to form a slow release fertilizer composition.
WO 2007/022031, Perez et al, discloses the use of interpenetrating polymer networks (IPN's) as protective coatings for metal surfaces. The IPN's are composed of polyolefins and epoxy resins.
US Appl 2010/0307211, to Xing, et al discloses fertilizer coatings that comprise a polyol, an isocyanate, a wax and an epoxidized fatty acid triglyceride. The epoxidized fatty acid triglyceride is added as a compatibilizer for the wax and polyol.
U.S. Pat. No. 5,803,946 to Petcavich, et al, discloses a controlled release coating for fertilizers that is described as an interpenetrating polymer network. It is comprised of a biuret, a urethane and tung oil interlinked one with another. The isocyanate is first applied to the fertilizer particles followed by a mixture of the polyol and tung oil and an initiator.
U.S. Pat. No. 8,303,680 to Mente, et al discloses polyurethane encapsulated fertilizer particles that comprise polymeric particles as a discontinuous phase in the polyurethane. The polymeric particles are from about 0.1 to about 10 microns in diameter. The polymeric particles disclosed are generally vinyl polymers that may incorporate urethane reactive monomers such as unsaturated polyols, to impart crosslinking to the polyurethane coating. The polymeric particles may also be polyurethanes. It is believed that the polymeric particles impart increased water repellency and resiliency to the encapsulated fertilizer particles.
U.S. Pat. No. 7,018,440 to Tabai discloses a granular fertilizer which is coated with a first water-insoluble material layer, a thermosetting resin layer, a second water-insoluble material layer, and a second thermosetting resin layer. The water-insoluble material layers are generally a wax and can be a mixture of petroleum wax and ethylene-vinyl acetate. The thermosetting resin can be urethane resin, epoxy resin, alkyl resin, unsaturated polyester resin, phenol resin, urea resin, melamine resin, silicone resin and the like.
U.S. Pat. No. 8,795,406 to Maruvada discloses a controlled release fertilizer comprising a particulate plant nutrient surrounded by a polyurethane coating consisting of a mixture of a cross-linked polyol and an isocyanate, and optionally an unsaturated wax. The polyol can be cross-linked with itself, with a triglyceride or with an unsaturated wax, by reaction with sulfur, oxygen, and/or a peroxide cross-linking moiety.
The need for a cooling step with agitation typically carried out in a fluid bed cooler or a rolling drum, particularly when a wax based sealant or wax based component is used in the coating process, adds costs and production space requirements to the coating process. It would be highly desirable to produce effective wax containing sealed free flowing granules without the need for a cooling step.